Multi-window display art is used to display various contents simultaneously in devices such as televisions, recorders, tablets and smartphones. Multi-window display is used for example to arrange and display the videos of multiple television broadcast channels within a single screen, or to display a television video with graphics used for interactive operation by a user in a data broadcast composed thereon.
Multi-window display may be realized for example by a method for rendering a virtual space video, wherein a plurality of image objects are pasted onto a plurality of surfaces of a virtual space object in accordance with a rendering scenario written for example using OpenGL.
Image objects displayed on the screen in multi-window display may be television videos which require decoding before being played back, therefore each image object must be stored in a memory until the image objects are composed on a single screen. Consequently, as the number of simultaneously displayed image objects increases the memory bandwidth required also increases. An increase in memory bandwidth is undesirable as it causes an increase in cost.
Patent Literature 1 describes an art for suppressing increases in the memory bandwidth required for multi-window display. In the disclosed art this is achieved by allotting a memory bandwidth to each image based on a rendering command which indicates the display form of the graphics or video. By scaling-down or the like, the resolution of each image is decreased to an appropriate level so that reading and writing of the memory can occur within the allotted memory bandwidth.